1. Field of the Invention
The present invention relates to a manufacturing method of a tuning-fork type quartz crystal resonator. More particularly, it relates to a manufacturing method of a tuning-fork type quartz crystal resonator, in which short-circuit of an electrode at a crotch portion is eliminated, and yield can be improved.
2. Description of the Related Art
A general constitution of a tuning-fork type quartz crystal resonator will be described with reference to FIG. 3. FIG. 3 is a schematic constitution diagram of the general tuning-fork type quartz crystal resonator.
As shown in FIG. 3, the general tuning-fork type quartz crystal resonator is formed by cutting out a single crystal of a quartz crystal, and constituted of a base portion 10 and two arm portions 11 and 12 protruding from the base portion 10.
Moreover, electrodes 13 and 14 formed of metal films are formed on a front surface portion and a back surface portion of the base portion 10. Here, the only front surface portion is shown, but the back surface portion is similarly formed.
Groove portions are formed in portions close to the base portion 10 at the front surface portion and the back surface portion of a quartz crystal 17 of the arm portion 11, and electrodes 15 formed of a metal film are disposed at the groove portions.
Similarly, groove portions and electrodes 16 are formed at the front surface portion and the back surface portion of a quartz crystal 18 of the arm portion 12. The electrodes 15 and 16 are also formed at outer surface portions and inner surface portions of the arm portions 11, 12.
In this manner, since the groove portions are disposed at the front surface portions and the back surface portions of the arm portions 11 and 12, the arm portions 11 and 12 have substantially H-shaped sections (not shown).
Furthermore, weight films 19 formed of metal films are disposed at the front surface portion and the back surface portion of the quartz crystal 17 at an end portion of the arm portion 11 on a side opposite to the base portion 10. Similarly, weight films 20 are disposed at the front surface portion and the back surface portion of the quartz crystal 18 of the arm portion 12.
Moreover, when a voltage is applied to the tuning-fork type quartz crystal resonator via the electrodes 13 and 14 of the base portion, the arm portions 11 and 12 vibrate to oscillate a predetermined frequency of, for example, 32.768 kHz.
However, with miniaturization of the tuning-fork type quartz crystal resonator, a short-circuit defect is easily generated in root portions of the arm portions 11 and 12.
The short-circuit defect will specifically be described with reference to FIG. 4. FIG. 4 is a schematic sectional explanatory view of a case where the short-circuit defect is generated at the A-A′ portion of FIG. 3.
As shown in FIG. 4, at the root portion (a crotch portion 30) of the arm portions 11 and 12, the arm portions 11 and 12 are formed from the base portion 10. Moreover, the electrode 15 is disposed at the inner surface portion of the arm portion 11, and the electrode 16 is formed at the inner surface portion of the arm portion 12.
In the tuning-fork type quartz crystal resonator, patterning is generally performed at a front and a back of a quartz crystal substrate by use of the same electrode and wiring line outer patterns, and electrode arrangements intersect with each other at the crotch portion 30. Therefore, the pattern at the crotch portion 30 becomes very complicated. It is to be noted that FIG. 4 is simplified in order to simplify description thereof.
Steps of forming the conventional electrodes 15 and 16 will briefly be described.
First, the quartz crystal substrate is processed into a tuning-fork form by machine processing and photography/etching, the groove portions of the arm portions 11 and 12 are further formed, and then the metal films constituting the electrodes are formed by vacuum evaporation or sputtering.
Then, after resists applied onto the metal films are exposed and developed into desired patterns by the photolithography, the metal films are patterned using the resist patterns as masks by etching. Afterward, the resists are peeled to form the electrodes 15 and 16. In the conventional manufacturing method of the tuning-fork type quartz crystal resonator, the electrodes 15 and 16 are formed in this manner.
In addition, since a crotch portion 30 part is a small area nipped between the arm portions 11 and 12 and further the pattern is complicated as described above, the exposure and development of the resist easily become insufficient as compared with another area (easily under-exposed and under-developed). Similarly, the metal films are easily under-etched.
Therefore, as shown in FIG. 4, a non-etched metal film portion 31 is easily generated at the crotch portion 30, and short-circuit occurs between the electrodes 15 and 16.
It is to be noted that examples of prior arts concerning the tuning-fork type quartz crystal resonator include Japanese Patent Application Laid-Open Nos. 2001-085963 (Patent Document 1), 08-139337 (Patent Document 2), 2003-133875 (Patent Document 3) and 2005-134364 (Patent Document 4).
In Patent Document 1, a constitution is described in which trim processing of irradiating the center of an arm portion with laser of 700 nm or less to remove a metal coating film is performed to regulate a frequency in the manufacturing method of a tuning-fork type quartz crystal resonator.
Especially, it is determined in Patent Document 1 that in a state in which individual piezoelectric vibration pieces (quartz crystal resonator elements) cut from a quartz crystal wafer are packaged in a sealed manner, a metal coating film portion is irradiated with laser light from a processing device to evaporate and remove a metal. Moreover, in Patent Document 2, there is described a constitution including the steps of forming a metal coating film for forming silicide, selectively reacting the metal coating film with an active layer to selectively form a silicide area in the active layer, and removing a non-reacted metal coating film in a preparing method of a semiconductor device.
In Patent Document 3, a constitution is described in which a metal coating film is irradiated with laser to form a pattern of a photo mask corresponding to the film in a manufacturing method of a tuning-fork type quartz crystal resonator, and in Patent Document 4, a constitution is described in which a dividing portion of an arm is irradiated with laser to remove the metal coating film in the manufacturing method of the tuning-fork type quartz crystal resonator.
However, the conventional manufacturing method of the tuning-fork type quartz crystal resonator has a problem that the short-circuit defect is easily generated at the crotch portion corresponding to a root of the arm portion.
Moreover, to prevent the short-circuit, process precision needs to be improved, and there has been a problem that manufacturing costs increase.